The immune system plays a major part in tumor pathogenesis. In animal models and in humans it has been demonstrated that tumor cell formation leads to T cell activation aimed at tumor cell destruction, while the development of cancer is related to specific tumor-specific anergy. Conditions of immunodeficiency, such as infection with HIV and prolonged immunosuppressive therapy are associated with an increased incidence of cancer formation. Several experimental and clinical immunomodulatory strategies are employed to activate a pro-inflammatory immune response in systemically disseminated tumors. Examples are numerous and include IL2 and IFN-α treatment in metastatic melanoma [Eigentler, T. K. et al., Lancet Oncol. 4(12):748-59 (2003)], IFN treatment in metastatic renal cell carcinoma [Gitlitz, B. J. and Figlin, R. A. Urol. Clin. North. Am. 30(3):589-600 (2003)], TNF-α therapy in metastatic thyroid carcinoma [Mitsiades, C. S. et al. Endocrinol. 178(2):205-16 (2003)], the use of granulocyte-colony-stimulating-factor (GCSF) as a dendritic cell activator in breast, prostate, and renal cancer [Waller, E. K. and Ernstoff, M. S. Cancer 1; 97(7):1797-809 (2003)], and transfer of alloreactive donor T lymphocytes to promote the ‘graft versus leukemia’ effect in hematological malignancies [Costello, R. T., et al., Eur. J. Haematol. 70(5):333-45 (2003)].
Leptin is an 18 kDa product of the ob gene that was discovered in 1994 [Zhang, Y. et al., Nature 372:425-432 (1994)]. This protein is secreted almost exclusively by adipose cells, and acts centrally at the hypothalamic region in regulating energy expenditure and appetite [Pelleymounter, M. A. et al., Science 269:540-543 (1995)]. Leptin deficient ob/ob mice suffer of morbid obesity, diabetes mellitus, hyperlipidemia and hepatic steatosis, while leptin administration to these mice results in reversal of these disorders [Halaas, J. L. et al., Science 269:543-546 (1995)]. In contrast, the administration of leptin to humans suffering from morbid obesity failed to suppress appetite or reduce weight [Friedman, J. M. et al., Nutr. Rev. 60(10 Pt 2):S1-14; discussion S68-84, 85-7 (2002)]. This disappointing result may stem from increased leptin levels in obese individuals, and ‘leptin resistance’ caused by other, newly discovered, regulatory proteins such as adiponectin [Mark, A. L. et al., J. Hypertens. 20(7):1245-50 (2002); Berg, A. H. et al., Trends Endocrinol. Metab. 13(2):84-9 (2002)].
It has been previously suggested that leptin possesses potent immunomodulatory properties [Loffreda, S. et al., 12(1):57-65 (1998)]. Structurally, leptin is similar to IL2, IL6, and IL15, making it a member of the helical cytokine superfamily [Madej, T. et al., FEBS Lett. 2; 373(1):13-8 (1995)], while leptin receptors are structurally similar to hematopoietic cytokine receptors [Gimble, J. M. et al., Bone 19(5):421-8 (1996)]. Leptin receptors are found on CD4 and CD8 lymphocytes, monocytes [Sanchez-Margalet, V. Clin. Exp. Immunol. 129(1):119-24 (2002)], natural-killer lymphocytes [Zhao, Y. et al., Biochem. Biophys. Res. Commun. 10:300(2):247-52 (2003); Motivala, S. J. et al., Alcohol. Clin. Exp. Res. 27(11):1819-24 (2003)], and hepatic stellate cells [Saxena, N. K. et al., Hepatology 35(4):762-71 (2002)]. Leptin enhances T cell proliferation and pro-inflammatory cytokine secretion [Lord, G. M. et al., Nature 27; 394(6696):897-901 (1998); Lord, G. M. et al., J. Leukoc. Biol. 72(2):330-8 (2002); Martin-Romero, C. et al., Cell. Immunol. 10; 199(1):15-24 (2000)], by activating the JAK/STAT signal transduction pathway [Cao, Q. et al., J. Biol. Chem. 6; 279(6):4292-304 (2004)]. Leptin deficient ob/ob mice are immune deficient, suffering from an increased propensity for infection and mortality [Faggioni, R. et al., FASEB J. 15(14):2565-71 (2001)] and impaired function of NKT lymphocytes and hepatic macrophages [Li, Z. et al., Gastroenterology 123(4):1304-10 (2002)]. These mice are resistant to several Th1 mediated immune disorders, including allergic experimental encephalomyelitis [Matarese, G. et al., J. Immunol. 15; 166(10):5909-16 (2001)], concanavalin A hepatitis [Siegmund, B. et al., Eur. J. Immunol. 32(2):552-60 (2002)], experimental arthritis [Busso, N. et al., J. Immunol. 15; 168(2):875-82 (2002)], and autoimmune nephritis [Tarzi, R. M. et al., Am. J. Pathol. 164(2):385-90 (2004)] but are extremely vulnerable to LPS-induced hepatic damage [Yang, S. et al., Am. J. Physiol. Gastrointest. Liver Physiol. 281(2):G382-92 (2001)]. Leptin replenishment reverses all of these disorders.
Wildtype mice that do not suffer from leptin deficiency develop a potentiation in severity of experimental allergic encephalomyelitis [Matarese, G. et al., Eur. J. Immunol. 31(5):1324-32 (2001)] and type I diabetes mellitus [Matarese, G. et al. Diabetes 51(5):1356-61 (2002)]. In humans, no trials have examined the relationship between leptin and immune phenomena. However, the elevated leptin levels among females (that also suffer from an unexplained increased tendency for the development of autoimmune disease) and the reduced levels of leptin among malnourished individuals (that also tend to develop secondary immune deficiency) may point out to leptin being a link between nutrition and immunity [Matarese, g. et al., Trends in immunology. 23(4):182-7 (2002)].
Aberrant leptin receptors have been found on breast [Hu, X. et al., J. Natl. Cancer. Inst. 20; 94(22):1704-11 (2002)], endometrial [Yuan, S. S. et al., Gynecol. Oncol. 92(3):769-75 (2004)], bladder [Yuan, S. S. et al., Urology. 63(2):408-13 (2004)], and esophageal [Somasundar, P. et al., Am. J. Surg. 186(5):575-8 (2003)] cancer cell lines. Leptin has been recently demonstrated to activate proliferation of breast [Catalano, S. et al., J. Biol. Chem. 25 (2004)], prostate [Onuma, M. et al., J. Biol. Chem. 24:278(43):42660-7 (2003)], pancreas [Somasundar, P. et al., J. Surg. Res. 113(1):50-5 (2003)], and colon [Rouet-Benzineb, P. et al., J. Biol. Chem. 29 (2004)] cancer cell lines through direct activation of JAK/STAT signal transduction pathway. Thus, leptin may exert two opposing effects—a direct, pro-proliferative effect on tumor cells and an indirect, pro-inflammatory and anti-tumoral immune response. The net balance between these two leptin-induced reactions may determine whether it may play a pro or anti tumorogenic effect.
The present invention shows a clear involvement of leptin in modulation of Th1 immune response, and pro-inflammatory cytokine secretion, particularly through NKT lymphocyte activation. Such modulation enables the use of leptin as an immunomodulator for the treatment of different immune-related disorders, particularly, disorders involving NK cells.
It is therefore an object of the invention to provide a method for the modulation of Th1-Th2 response, and more particularly to enhance a pro-inflammatory cytokine secretion.
Another object of the invention is to provide method for the treatment immune-related disorders by modulating the expression of leptin.
The invention further provides for the use of leptin in the treatment of immune-related disorders and in immuno-modulation.
These and other objects of the invention will become apparent as the description proceeds.